The continuing development of portable electrically powered devices such as tape recorders and playback machines, radio transmitters and receivers, and the like, create a continuing demand for th development of reliable, long service life cells or batteries for their operations. Recently developed electrochemical cell systems that will provide a long service life utilize highly reactive anode materials such as lithium, sodium and the like, in conjunction with high energy density nonaqueous liquid cathode materials and a suitable salt.
It has recently been disclosed in the literature that certain materials are capable of acting both as an electrolyte carrier, i.e., as solvent for the electrolyte salt, and as the active cathode for a nonaqueous electrochemical cell. U.S. Pat. No. 4,400,453 discloses a nonaqueous electrochemical cell comprising an anode, a cathode collector and a cathode-electrolyte, said cathode-electrolyte comprising a solution of an ionically conductive solute dissolved in an active cathode depolarizer wherein said active cathode depolarizer comprises a liquid oxyhalide of an element of Group V or Group VI of the Periodic Table. The "Periodic Table" is the Periodic Table of Elements as set forth on the inside back cover of the Handbook of Chemistry and Physics, 63rd Edition, CRC Press Inc., Boca Raton, Fla., 1982-1983. For example, such nonaqueous cathode materials would include sulfuryl chloride, thionyl chloride, phosphorous oxychloride, thionyl bromide, chromyl chloride, vanadyl tribromide and selenium oxychloride.
Another class of liquid cathode materials would be the halides of an element of Group IV to Group VI of the Periodic Table. For example such nonaqueous cathode material would include sulfur monochloride, sulfur monobromide, selenium tetrafluoride, selenium monobromide, thiophosphoryl cloride, thiophosphoryl bromide, vanadium pentafluoride, lead tetrachloride, titanium tetrachloride, disulfur decafluoride, tin bromide trichloride, tin dibromide dichloride and tin tribromide chloride.
However, one possible drawback to the use of a liquid cathode such as thionyl chloride is that if it is not uniformly distributed along the surface of an anode, such as lithium, via a separator, then nonuniform anode consumption could occur and may result in low voltage output, particularly at high discharge rates, and longer voltage delays after storage. In addition, nonuniform distribution of the liquid cathode could cause nonuniform anode dissolution. This nonuniform anode dissolution causes high points and plateaus to form on the anode which may possibly result in localized heating during charging (abuse condition) and might lead to the possibility of anode melting at these discrete points. This could lead to a violent venting of the cell or even to cell disassembly.
To optimize the uniform absorption of large amounts of a liquid cathode onto and into a separator, a coiled electrode assemby should be employed. In U.S. Pat. No. 3,809,580, a nonaqueous hermetically sealed cell is disclosed which employs a coiled electrode assembly. Specifically, the negative electrode comprises lithium metal pressed onto a fine copper screen (anode collector) which is insulated from the cathode by a separator of porous polyethylene. The cathode is a passive electrode (cathode collector) formed by conductive carbon mixed with glass fibers and polytetrafluoroethylene which acts as a binder, the mixture being pressed into a fine aluminum screen which acts as a cathode collector. The cathode-electrolyte used in the cell is a solution of sulfur dioxide, a cosolvent of an anhydrous organic liquid such as methylformate and a solute of lithium bromide or the like. The cathode-electrolyte solution is pressure injected into the cell through a nipple in the conventional manner. Although the components of this type of cell construction are suitable for cathode-electrolytes employing sulfur dioxide as the principle active cathode material, they would not be suitable for cathode-electrolytes employing liquid oxyhalides as disclosed in U.S. Pat. No. 4,400,453 since the oxyhalides are extremely corrosive and react with and/or dissolve many of the cell components of the prior art such as aluminum, copper, polyethylene and the like.
In British Patent No. 1,542,690, a nonaqueous cell is disclosed comprising a coiled assembly of a cathode collector sheet, an active metal anode sheet, i.e. lithium, and a nonwoven glass separator interposed between said cathode collector sheet and said anode sheet, and a cathode-electrolyte comprising a solution of an ionically conductive solute dissolved in a liquid cathode such as an oxyhalide of an element of Group V or Group VI of the Periodic Table.
If the cathode collector in these types of cell constructions is positioned to contact the wall of the cell container and the anode, such as lithium, is placed within the cathode collector, then heat from an external source must be transmitted through the cathode collector and liquid catode-electrolyte before it reaches the anode. During this period, the internal pressure will substantially increase prior to any melting of the anode and the high pressure could be released through a suitable vent before any thermal reaction occurs. In cells where the anode is disposed next to the wall of the container, the anode may melt from exposure to external heat and react with the liquid cathode-electrolyte before the internal pressure is high enough to open a vent system. Although a cell employing the external cathode collector construction is safer than a cell employing the external anode construction, the placing of the cathode collector against the wall of the container will adapt the container as the cathodic terminal, thereby restricting the material that can be employed as the container. Specifically, when the container contacts the cathode collector it becomes the cathodic terminal and is thereby subject to corrosion and chemical attack by the cathode-electrolyte.
It is an object of the present invention to provide a liquid cathode cell system with a coiled electrode assembly that is safe to operate and that can be assembled with various types of container materials.
It is another object of the present invention to provide a liquid cathode cell system with a coiled electrode assembly that has the safety feature of having an external cathode construction while at the same time being adapted for providing anodic protection for the container of the cell.
It is another object of the present invention to provide a liquid cathode cell system with a coiled electrode assembly in which the catohde collector is disposed outside of the anode and in which the anode collector is extended to contact the container of the cell so as to provide anodic protection for the container of the cell.